Magnetic recording (“MR”) media and devices incorporating same are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval applications, typically in disk form. Conventional magnetic thin-film media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation of the magnetic domains of the grains of magnetic material.
A portion of a conventional longitudinal recording, hard disk-type magnetic recording medium 1 commonly employed in computer-related applications is schematically illustrated in FIG. 1, and comprises a substantially rigid, non-magnetic metal, glass, ceramic, glass-ceramic, or polymeric substrate 10, typically of aluminum (Al) or an aluminum-based alloy, such as an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited or otherwise formed on a surface 10A thereof a plating layer 11, such as of amorphous nickel-phosphorus (Ni—P); a seed layer 12A of an amorphous or fine-grained material, e.g., a nickel-aluminum (Ni—Al) alloy, a chromium-titanium (Cr—Ti) alloy, a tantalum (Ta) layer, or a tantalum nitride (TaN) layer; a polycrystalline underlayer 12B, typically of Cr or a Cr-based alloy, a magnetic recording layer 13, e.g., of a cobalt (Co)-based alloy with one or more of platinum (Pt), Cr, boron (B), etc.; a protective overcoat layer 14, typically containing carbon (C), e.g., a diamond-like carbon (“DLC”); and a lubricant topcoat layer 15, e.g., of a perfluoropolyether. Each of layers 11–14 may be deposited by suitable physical vapor deposition (“PVD”) techniques, such as sputtering, and layer 15 is typically deposited by dipping or spraying.
In operation of medium 1, the magnetic layer 13 is locally magnetized by a write transducer, or write “head”, to record and thereby store data/information therein. The write transducer or head creates a highly concentrated magnetic field which alternates direction based on the bits of information to be stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the material of the recording medium layer 13, the grains of the polycrystalline material at that location are magnetized. The grains retain their magnetization after the magnetic field applied thereto by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium layer 13 can subsequently produce an electrical response in a read transducer, or read “head”, allowing the stored information to be read.
Efforts are continually being made with the aim of increasing the areal recording density, i.e., the bit density, or bits/unit area, and signal-to-medium noise ratio (“SMNR”) of the magnetic media. However, severe difficulties, such as thermal instability, are encountered when the bit density of longitudinal media is increased above about 20–50 Gb/in2 in order to form ultra-high recording density media, because the necessary reduction in grain size reduces the magnetic energy, Em, of the grains to near the superparamagnetic limit, whereby the grains become thermally unstable. Such thermal instability can, inter alia, cause undesirable decay of the output signal of hard disk drives, and in extreme instances, result in total data loss and collapse of the magnetic bits.
One proposed solution to the problem of thermal instability arising from the very small grain sizes associated with ultra-high recording density magnetic recording media, is to increase the crystalline anisotropy and therefore increase the magnetic energy of the grains, thus the squareness of the magnetic bits, in order to compensate for the smaller grain sizes. However, this approach is limited by the field provided by the writing head.
Another proposed solution to the problem of thermal instability of very fine-grained magnetic recording media is to provide stabilization via coupling of the ferromagnetic recording layer with another ferromagnetic layer or an anti-ferromagnetic layer. In this regard, it has been recently proposed (E. N. Abarra et al., IEEE Conference on Magnetics, Toronto, April 2000) to provide a stabilized magnetic recording medium comprised of at least a pair of spaced-apart ferromagnetic layers which are anti-ferromagnetically-coupled (“AFC”) by means of an interposed thin, non-magnetic spacer layer. RKKY-type coupling between the spaced-apart magnetic layers is presumed to increase the effective volume of each of the magnetic grains, thereby increasing their stability; the coupling strength J between the ferromagnetic layer pairs being a key parameter in determining the increase in stability.
Notwithstanding the improvements in performance of ultra-high areal density magnetic recording media provided by the anti-ferromagnetically coupled main recording and stabilization layers as described supra, further improvement of AFC media performance, e.g., SMNR and bit error rate, is desired.
Accordingly, there exists a need for improved thermally stable, high areal density anti-ferromagnetically coupled (AFC) magnetic recording media and manufacturing methodology therefor, with enhanced RKKY-type coupling providing improved thermal stability and performance characteristics, such as signal-to-media noise ratio (SMNR) and bit error rate, which media can be fabricated at a cost competitive with that of conventional manufacturing technologies for forming high areal density AFC-type magnetic recording media. There also exists a need for improved, high areal density, AFC-type magnetic recording media, e.g., in disk form, which media include vertically spaced-apart, anti-ferromagnetically coupled ferromagnetic alloy layers separated by a non-magnetic spacer layer, wherein RKKY-type coupling between the spaced-apart magnetic layers is enhanced vis-a-vis conventionally structured AFC media and the media exhibit improved thermal stability and performance characteristics.
The present invention, therefore, facilitates cost-efficient manufacture of high areal recording density, thermally stable, high SMNR, low bit error rate AFC magnetic recording media, e.g., in the form of hard disks, while providing full compatibility with all aspects of conventional automated manufacturing technology. Moreover, manufacture and implementation of the present invention can be obtained at a cost comparable to that of existing technology.